1. Field of the Invention
The present invention relates to a detecting apparatus of vehicle speed preferably used in a navigation apparatus for vehicle mounting or the like.
2. Description of the Related Art
A navigation apparatus for vehicle mounting is constituted as shown by, for example, FIG. 1. That is, in FIG. 1, there is provided a microcomputer 10 as a control circuit for controlling operation of a total of the navigation apparatus. The microcomputer 10 includes CPU (Central Processing Unit) 11 for executing various programs, ROM (Read Only Memory) 12 written with the programs, RAM (Random Access Memory) 13 for work area and an involatile memory 14 for holding various data and further includes an interface circuit 16 and an LCD (Liquid Crystal Display) controller 17, which are connected to each other via a system bus 19.
Further, the interface circuit 16 is connected with various operation keys (operation switches) 15 and the LCD controller 17 is connected with a color LCD 18.
Further, the navigation apparatus of FIG. 1 is a case of further using DVD (Digital Versatile Disc)xe2x80x94ROM 21 as medium of large capacity having map data, that is, DVD-ROM 21 is contained with various map data necessary for navigation. Further, there is provided a DVD-ROM drive apparatus 22 for reading data from DVD-ROM 21 and the drive apparatus 22 is connected to the system bus 19.
Further, radio wave from a navigation satellite, for example, a GPS (Global Positioning System) satellite is received by a GPS antenna 23 and a received signal thereof is supplied to a GPS unit (receiving circuit) 24, data of a position of its own is outputted from the GPS unit 24 and the data is supplied to the microcomputer 10.
Further, a self-contained navigation unit, for example, a gyro 25 is provided, data in a direction of moving the vehicle per se is outputted from the gyro 25 and the data is supplied to the microcomputer 10. Further, a vehicle speed sensor for detecting traveling speed of the vehicle is provided and an output signal thereof is supplied to the microcomputer 10.
According to such constitution, output signals from the GPS unit 24, the gyro 25 and the vehicle speed sensor 26 are processed by CPU 11 to thereby determine a position of the vehicle of its own and map data of a map including the position of the vehicle of its own is read from DVD-ROM 21. Further, LCD 18 displays an electronic map centering on a vicinity of the position of the vehicle of its own in accordance with the read map data and displays, for example, a triangular mark (xcex94) indicating the vehicle of its own at the position of the vehicle of its own.
Further, in this case, the position of the vehicle of its own can be determined with considerable accuracy only by the GPS unit 24; however, radio wave from the GPS satellite may not be received behind a building or in a tunnel. In such an occasion, determination of the position of the vehicle of its own becomes inaccurate or cannot be carried out at all.
Hence, the navigation apparatus of FIG. 1 is provided with the gyro 25 and the vehicle speed sensor 26, thereby, even when radio wave from the GPS satellite cannot be received, the position of the vehicle of its own can be determined.
Further, as a method of detecting the traveling speed of the vehicle by the vehicle speed sensor 26, there are reduced into practice:
(1) outputting a speed signal from a signal cable reaching a speedometer of the vehicle;
(2) detecting rotational speed of tire, that is, traveling speed by magnetizing tire by a magnet and detecting the magnetism by a magnetic sensor.
However, in the case of the method in item (1), it is considerably difficult for a general user to execute operation for the reasons of:
it is necessary to strip an inner lining of the vehicle;
wiring of the signal cable differs by vehicle kind;
it is necessary to find the signal cable from a number of similar cables.
Therefore, sales routes of navigation apparatus are limited to special stores and expensive attaching fee is needed, which constitutes factors for hampering spread of the navigation apparatus.
Further, in the case of the method in item (2), a power supply cable and a signal cable are needed for the magnetic sensor and these cables must be led between the magnetic sensor arranged at outside of the vehicle and the navigation apparatus arranged at inside of the vehicle, and so the operation requires time and labor. Further, since tire cannot be magnetized strongly, the magnetic sensor for detecting the magnetism needs to be provided with high sensitivity. As a result, error is increased when the vehicle is passing a steel bridge or traveling at a vicinity of a railroad.
It is an object of the invention to solve the above-described problem.
According to an aspect of the invention, there is provided, for example, a detecting apparatus of vehicle speed comprising:
detecting means for emitting an electromagnetic wave or an ultrasonic wave to a road surface and detecting traveling speed of a vehicle from the Doppler effect produced in a reflected wave thereof;
a transmitting circuit for sending information about the traveling speed detected by the detecting means by radio;
a power generation mechanism for generating power by vibration produced in the vehicle; and
a charging circuit for charging a charging type battery by an output voltage of the power generation mechanism;
wherein voltage of the charging type battery is supplied to the detecting means and the transmitting circuit as operating voltage thereof.
Therefore, it is not necessary to connect a power supply cable to the speed detecting apparatus, and it is not necessary to connect a cable for informing the navigation apparatus of the detected traveling speed, and so the transmission becomes wireless. Accordingly, attachment of the speed detecting apparatus to the vehicle is simplified. Further, it is not that the sales routes are limited to special stores or expensive attachment fee is needed as in the conventional navigation apparatus, and the speed detecting apparatus can be sold in a general household electric appliance store and is expedited to spread. Further, detection of vehicle speed can be carried out with high accuracy.
Further, when the vehicle is disposed in a garage or a parking lot and does not travel, consumption of the charging type battery constituting a source of operating voltage can be saved.